Small Cell Uplink Interference Mitigation

1. A method for identifying a user device being served by a first base station of a cellular network and causing radio interference in the uplink of a second base station, the method comprising, by the first base station: transmitting configuration information for the first base station to the second base station, wherein the configuration information comprises an identification of one or more resources allocated to an uplink channel of the first base station; receiving an interference indication message from the second base station, the interference indication message comprising an indication that a cell of the second base station is experiencing uplink interference from at least one interfering user device; for each of a plurality of user devices being served by the first base station, assigning a preamble to the user device; transmitting the preambles assigned to the plurality of user devices to the second base station; for each of the plurality of user devices, transmitting a message comprising the preamble, assigned to the user device, to the user device; receiving an information element from the second base station, wherein the information element comprises a list of one or more preambles which were detected at the second base station, on an uplink channel, from one or more preamble transmissions of one or more of the plurality of user devices, and a received signal strength for each of the one or more preambles which were detected at the second base station, and wherein identifying the at least one interfering user device is also based, at least in part, on the received signal strengths; and identifying the at least one interfering user device based, at least in part, on the list of preambles.

2. The method of claim 1 , further comprising, for each of the plurality of user devices, further assigning one of a plurality of preamble transmission times to the user device, wherein the message transmitted to the user device further comprises the assigned preamble transmission time.

3. The method of claim 2 , wherein the uplink channel is a Physical Random Access Channel (PRACH) of the first base station, and wherein the message transmitted to each of the plurality of user devices comprises a Physical Downlink Control Channel (PDCCH) order that causes the user device to initiate a Random Access (RA) procedure by transmitting the assigned preamble at the assigned preamble transmission time.

4. The method of claim 3 , further comprising, by the second base station: receiving one or more preambles from one or more user devices on the PRACH of the first base station using the identification of one or more resources; and transmitting the information element, comprising the received one or more preambles as the list of one or more preambles, to the first base station.

5. The method of claim 4 , further comprising, by the second base station detecting the signal strength of each of the received one or more preambles, wherein the transmitted information element further comprises the detected signal strength for each preamble in the list of one or more preambles.

6. The method of claim 1 , further comprising, by the first base station, for each of the plurality of user devices: estimating timing advance information comprising a transmission delay between the user device and the second base station; and transmitting the estimated timing advance information to the user device.

7. The method of claim 6 , wherein estimating timing advance information comprises: determining a location of the user device; determining a location of the second base station; and estimating a propagation distance between the user device and the second base station.

8. The method of claim 1 , wherein each assigned preamble is unique from the other assigned preambles.

9. The method of claim 1 , further comprising, by the first base station, performing at least one corrective action.

10. The method of claim 9 , wherein the at least one corrective action comprises one or more of initiating a handover procedure of the at least one interfering user device from the first base station to the second base station, and initiating a handover procedure of the at least one interfering user device from a first radio carrier to a second radio carrier.

11. The method of claim 1 , further comprising, by the first base station, for each assigned preamble, storing an association between the preamble and the assigned user device, and wherein identifying the at least one interfering user device comprises identifying an association between at least one of the one or more preambles in the list of one or more preambles and a user device assigned to the at least one preamble.

12. The method of claim 1 , further comprising, by the first base station, selecting the plurality of user devices, wherein the plurality of user devices consists of fewer than all user devices being served by the first base station.

13. The method of claim 1 , further comprising, by the first base station, transmitting to the second base station an identification of one or more resources to be used for preamble transmissions by the plurality of user devices.

14. The method of claim 1 , wherein the interference indication message comprises an indication that uplink interference is occurring on a particular carrier.

15. A system for mitigating interference at a base station of a cellular network by identifying an interfering user device, the system comprising a first base station configured to: transmit configuration information for the first base station to a second base station, wherein the configuration information comprises an identification of one or more resources allocated to an uplink channel of the first base station; receive an interference indication message from the second base station, the interference indication message comprising an indication that a cell of the second base station is experiencing uplink interference from at least one interfering user device; for each of a plurality of user devices being served by the first base station, assign a preamble to the user device; transmit the preambles assigned to the plurality of user devices to the second base station; for each of the plurality of user devices, transmit a message comprising the preamble, assigned to the user device, to the user device; receive an information element from the second base station, wherein the information element comprises a list of one or more preambles which were detected at the second base station, on an uplink channel, from one or more preamble transmissions of one or more of the plurality of user devices, and a received signal strength for each of the one or more preambles which were detected at the second base station, and wherein identifying the at least one interfering user device is also based, at least in part, on the received signal strengths; and identify the at least one interfering user device based, at least in part, on the list of preambles.

16. The system of claim 15 , wherein the first base station is further configured to, for each of the plurality of user devices, assign one of a plurality of preamble transmission times to the user device, wherein the message transmitted to the user device further comprises the assigned preamble transmission time.

17. The system of claim 16 , wherein the uplink channel is a Physical Random Access Channel (PRACH) of the first base station, and wherein the message transmitted to each of the plurality of user devices comprises a Physical Downlink Control Channel (PDCCH) order that causes the user device to initiate a Random Access (RA) procedure by transmitting the assigned preamble at the assigned preamble transmission time.

18. The system of claim 17 , further comprising the second base station, wherein the second base station is configured to: receive one or more preambles from one or more user devices on the PRACH of the first base station using the identification of one or more resources; and transmit the information element, comprising the received one or more preambles to the first base station as the list of preambles, to the first base station.

19. The system of claim 18 , wherein the second base station is further configured to detect the signal strength of each of the received one or more preambles, wherein the transmitted information element further comprises the detected signal strength for each preamble in the list of one or more preambles.

20. The system of claim 15 , wherein the first base station is further configured to, for each of the plurality of user devices: estimate timing advance information comprising a transmission delay between the user device and the second base station; and transmit the estimated timing advance information to the user device.

21. The system of claim 20 , wherein estimating timing advance information comprises: determining a location of the user device; determining a location of the second base station; and estimating a propagation distance between the user device and the second base station.

22. The system of claim 15 , wherein each assigned preamble is unique from the other assigned preambles.

23. The system of claim 15 , wherein the first base stations is further configured to perform at least one corrective action.

24. The system of claim 23 , wherein the at least one corrective action comprises one or more of initiating a handover procedure of the at least one interfering user device from the first base station to the second base station, and initiating a handover procedure of the at least one interfering user device from a first radio carrier to a second radio carrier.

25. The system of claim 15 , wherein the first base station is further configured to, for each assigned preamble, store an association between the preamble and the assigned user device, and wherein identifying the at least one interfering user device comprises identifying an association between at least one of the one or more preambles in the list of one or more preambles and a user device assigned to the at least one preamble.

26. The system of claim 15 , wherein the first base station is further configured to select the plurality of user devices, wherein the plurality of user devices consists of fewer than all user devices being served by the first base station.

27. The system of claim 15 , wherein the first base station is further configured to transmit to the second base station an identification of one or more resources to be used for preamble transmissions by the plurality of user devices.

28. The system of claim 15 , wherein the interference indication message comprises an indication that uplink interference is occurring on a particular carrier.